The present invention relates to a nozzle blade angle adjustment device for a variable geometry turbocharger.
In order to improve heat efficiency of various prime movers, turbochargers used to date are of the type in which a turbine is rotated by exhaust gases from a prime mover to drive a compressor which in turn compresses and charges air into the prime mover.
With the turbocharger of this type, the flow rate of exhaust gases used as a power source varies in response to variation in load on the prime mover. Therefore, such a variable geometry turbocharger has been devised and demostrated as described in U.S. Pat. No. 4,741,666 which has a device for adjusting, in response to a load on a prime mover, angles of nozzle blades for guiding exhaust gases to a turbine wheel.
Such a nozzle blade angle adjustable device will be explained in more detail with reference to FIGS. 1 and 2.
A turbocharger comprises a turbine 1 and a compressor 2 connected through a bearing casing 3 to the turbine 1.
The turbine 1 includes a casing 4 and a gas outlet cover 5 which clamp together a shroud 6 which in turn rotatably supports each nozzle shaft 7 through a bearing 8. The shaft 7 has a nozzle blade 9 at its one end adjacent to the casing 4 and has a nozzle link 10 at its other end adjacent to the cover 5.
The cover 5 and shroud 6 define together a space 12 which is in the form of a doughnut to surround a gas outlet 11 and which accommodates a rotatable nozzle drive ring 13 in addition to the nozzle links 10. The ring 13 has a pins 14 and slide joints 15 both extending from the ring 13. The joint 15 is radially slidably fitted into a slide groove 16 defined at one end of the corresponding link 10. The ring 13 has also a pin 17 and a slide joint 18 both extending from the ring 13. The joint 18 is radially slidably fitted into a guide groove 20 at one end of a drive link 19. The drive link 19 is securely attached at its rear end to one end of a drive shaft 22 which passes through the cover 5 through a bearing 21. The other end of the shaft 22 is connected to a drive lever 23. Reference mumeral 24 designates a turbine wheel; 25, a compressor wheel; 26, a turbine shaft; 27, a water jacket; 28, and oil supply opening; 29, an oil discharge opening; and 30, guides for guidance of the rotating ring 13.
When the drive lever 23 is driven by an external power source, the nozzle ring 13 is caused to rotate through the shaft 22 and the link 19. In response to the degree of rotation of the ring 13, the angles of all of the nozzle blades 9 are simultaneously varied through the nozzle links 10.
With the conventional nozzle blade angle adjustment device just described above, the device itself rises in temperature in excess of 500.degree. C. during operation and is in a turbine which is too high in temperature to lubricate (since any lubricating oil supplied would be carbonized due to the high temperature). As a result, the following problems arise.
Slide elements slidable in the radial direction of the ring 13 and thus of the turbine wheel 24 such as the slide joints 15 and 18 and the slide guide grooves 16 and 20 are adversely affected by oxidation at high temperature as well as wear caused by slide motion. As a result, the surface of the slide element is covered with fragile, oxidized layer due to oxidization at high temperature and said oxidized layer is readily worn out due to the slide contact. This is repeated many times, resulting in breakdown of the slide elements. Consequently the reliability of the device is not satisfactorily ensured because of its low durabililty.
In view of the above, a primary object of the present invention is to provide a nozzle blade angle adjustment device for a variable geometry turbocharger which can be installed at low temperature portions and can be cooled to reduce adverse effects due to oxidization at high temperatures and which has no slide elements slidable in the radial direction of a turbine wheel and liable to receive slide wear, thereby enhancing the durability and realiability of the device.